1. Field of the Invention
The present invention relates to a hydraulic control device for poppet valves of combustion engines, comprising a valve with a valve spring and a hydraulic closed system, that is formed by a cam input cylinder and a valve-actuating cylinder which are connected by a connecting line, wherein a cam input piston guided in the cam input cylinder is actuated by a cam and a valve-actuating piston guided in the valve-actuating cylinder is functionally connected to the valve, and further comprising a main lubricating device which is connected in parallel to the hydraulic closed system via a relief valve.
2. Description of the Prior Art
A poppet valve for combustion engines, which may be opened by a hydraulic valve-actuating piston and closed by a valve spring, has been known from DE-OS 31 15 423. The valve-actuating piston is actuated by the hydraulic fluid via a cam input cylinder which is engaged by a cam, whereby the cam input cylinder of the cam input piston is connected to the valve-actuating cylinder of the valve-actuating piston via a connecting duct. In order to compensate for oil leakage, the hydraulic closed system, consisting of a cam input cylinder, a valve-actuating cylinder, and the connecting duct, is connected with a common main lubricating device. To avoid backflow of the hydraulic fluid, a relief valve is arranged between the hydraulic closed system and the main lubricating device.
A disadvantage of such a hydraulic valve control device is that the valve movement is rigidly coupled to the given movement of the cam.
It is therefore an object of the present invention to provide a valve control device being variable with respect to the movement imposed by the cam.